The present invention relates to a transducer bridge circuit arrangement. More specifically, the present circuit arrangement comprises a plurality of bridge circuit configurations arranged in parallel to each other. Each bridge circuit configuration comprises four strain gauges forming, for example, a bending strain transducer or a shearing strain transducer.
It is well known in the art of electrically measuring mechanical quantities to connect a plurality of transducers in parallel to each other. For example, U.S. Pat. No. 2,866,059 granted to Eric Laimins discloses transducers that may be connected in parallel to each other. The need for connecting transducers in parallel to each other exists, for example, in connection with a platform scale wherein one transducer is operatively interposed between the support structure and each corner of the scale platform.
In order to reduce the costs of such transducers, it is customary to permit a relatively wide range of sensitivity variations or a wide output calibration tolerance for each transducer of the same type. Such tolerance may be within the range of .+-. 15%. Due to this broad calibration tolerance range, it is necessary to adjust the sensitivity of the transducers of the same scale so that each transducer will provide the same output signal. Without such sensitivity adjustment, any one of these transducers may vary within the above tolerance range in its output signal thereby preventing an accurate weighing. Heretofore it was customary to connect a resistor, for example, in adjustable resistors such as a potentiometer in series with the transducer of a set of transducer. Such resistors were used particularly in series with the high output transducer to reduce that output down to that of the other transducers of the same set of transducers. However, the use of such series resistors in one transducer also affects the sensitivity of the other transducers in the same set as will be described in more detail below. Due to such interaction it was necessary heretofore to repeatedly readjust the transducers of a set of transducers until each transducer in a set would exhibit the desired sensitivity. Such repeated adjustments are time consuming and hence expensive. Moreover, even repeated adjustments do not eliminate the just described undesirable interaction. It would be desirable that the sensitivity of each transducer in a set can be adjusted independently of the sensitivity of any other transducers in a set.